Implant for transforaminal interbody fusion

ABSTRACT

The invention relates to an implant for the transforaminal intracorporeal fusion of lumbar vertebral column segments. At least some sections of the surface areas that are in direct contact with the spinal column are provided with an anti-dislocation mechanism ( 1 ) while an attachment part ( 4 ) for a positioning instrument ( 10 ) is provided in or on the implant and holes ( 6 ) or hollow spaces are disposed in the implant for filling purposes. According to one embodiment of the invention, the attachment part is configured as a revolute joint. In a further embodiment, the implant member has the shape of a sickle, the curvature of which is oriented ventrally and the interior of which is oriented dorsally. The attachment part is located at one end of the sickle while the opposite end of the sickle has a beak-type, tapering shape ( 5 ). At least one filling hole is provided between the sickle walls.

BACKGROUND OF THE INVENTION Field of the Invention

The invention relates to an implant for the transforaminal interbodyfusion of lumbar vertebral column segments.

Attempts are made to use minimal invasive surgery for spine operations.To this end, so-called PLIF (posterior lateral interbody fusion)operation techniques were developed. According to such an operationtechnique the intervertebral disc is removed through a posterior access,and the intervertebral space is filled with autologous bone. Thistechnique is based on Cloward, who was the first to carry through suchan operation in 1943. Further developments of the PLIF techniqueresulted in the application of a transforaminal access. This techniqueprovides for the dorsal, transforaminal introduction of titaniumcups—so-called cages—which are filled with autologous cancellous bone.At the same time, a dorsal instrumentation and stabilization is applied.The advantage of the briefly outlined method is that no transabdominalor retroperitoneal additional access has to be used.

The “Biotit Cage” of the company Ulrich serves to replace anintervertebral disc of the lumbar vertebral column. The cage is insertedthrough a dorsal access, with the application being possible in pairs orindividually. This prior cage is substantially U-shaped and comprises adislocation protection in the form of a striated structure. The implantmaterial of the aforementioned cage is titanium or a titanium alloy,respectively, so that relatively large radiological windows arenecessary to control the fusion.

Further known is a cage distributed by the company Stryker Orthopaedic,U.S.A., which is a cubic implant and can be implanted in pairs into theintervertebral space by an anterior as well as a posterior approach.

As regards the prior art, reference is additionally made to DE 43 28 062A1, which relates to an implant for the replacement of vertebral bodiesand/or the stabilization and fixation of the vertebral column. Thisimplant consists of an implant body which is pushed onto a support rodtransversely to the axis of the rod. The implant body according to DE 4328 062 A1 is provided with a surface structure bearing against thevertebral bodies adjacent to the implant, so as to achieve a mutualfixation of the adjacent surfaces of the implant body on the one handand the vertebral body on the other hand.

The prior art likewise includes height-adjustable vertebral bodyimplants for the replacement of one or more vertebral bodies, e.g.according to DE 44 23 257 A1, DE 195 19 101 A1 or DE 195 09 317 A1.However, the production of these height-adjustable implants is veryexpensive, and their handling is complicated.

In the German utility model DE 296 16 778 U1 a vertebral bodyreplacement is disclosed, which is inserted, for example, after avertebral body resection to replace the missing vertebral body. Suchreplacements are made of a body-compatible material, with the front endsforming an irregular edge and the wall of the replacement having holesto provide for enough space to receive bone substance.

To insert the replacement according to DE 296 16 778 U1, a tool having arelatively long shank is used, with the shank having a threaded journalon the free end thereof to be brought into engagement with a threadedhole of the sleeve-shaped body so as to insert the same into the spaceof the resected vertebral body, in the predefined position between twoadjacent vertebral bodies.

OBJECTS AND SUMMARY OF THE INVENTION

Based on the foregoing it is the object of the invention to provide afurther developed implant for the transforaminal interbody fusion oflumbar vertebral column segments. The implant is to have a high primarystability and allows a simple operative procedure in use.

The solution to the object of the invention is achieved with an implantaccording to the combination of features defined in patent claim 1. Morespecifically, an implant for the transforaminal interbody fusion oflumbar vertebral column segments is provided in accordance with thepresent invention, wherein at least some sections of the surface areascoming into direct contact with the vertebral column are provided with adislocation protection, wherein further an engagement part for apositioning instrument is provided in or on the implant, and holes orhollow spaces are disposed in the implant for filling purposes. Thedependent claims comprise at least expedient embodiments andadvancements. Additionally claimed is a specific positioning instrumentfor such an implant, which is defined in patent claim 8.

Proceeding from an implant of which at least some sections of thesurface areas coming into direct contact with the vertebral column areprovided with a dislocation protection and which is provided with anengagement part for a positioning instrument, the further developedimplant body has the shape of a sickle, with the convexity of the sicklebeing oriented ventrally and the inner side of the sickle being orienteddorsally.

The specific engagement part, which acts like a pivot joint, is locatedon one end of the sickle, while the opposite end of the sickle has abeak-like, tapering shape which serves as an insertion aid. At least onefilling hole for receiving a large amount of bone substance is providedbetween the sickle walls of the implant body.

In one embodiment of the invention the engagement part is formed as arotatable or pivotable bolt received in a through bore, the bolt havingan insertion opening for an instrument which extends perpendicular tothe longitudinal axis.

The sickle end with the engagement part is provided with a recessserving as access to the bolt and to the insertion opening for theaforementioned positioning instrument.

Preferably, the implant is made of a bioelastic synthetic material,specifically polyetheretherketone (PEEK). However, other appropriateimplant materials are usable as well.

X-ray markers are incorporated in the bioelastic synthetic material. Inthe ventral, medial part these X-ray markers may be oriented vertically,while the orientation may be a horizontal, sagittal one at the implanttip.

Moreover, it is possible according to the invention to construct thebolt as a rotary part made of an X-ray detectable material.

Preferably, the structures of the dislocation protection have the shapeof a truncated pyramid or truncated cone, or are realized in the form ofspherical, cut bodies.

In a preferred embodiment of the invention the insertion opening of thebolt has an inner thread.

The positioning instrument used for handling the above-described implantis comprised of a shank and a sleeve, wherein the sleeve receives a pinwith a threaded end and the threaded end is designed complementarilywith respect to the inner thread of the insertion opening in the bolt.

Moreover, the pin with the threaded end can be moved by a rotary motionto be longitudinally displaceable relative to the sleeve. At the leadingend of the sleeve a stopping face for the implant is provided, so thatthe implant held by the pin is fixable in the respective angularposition by means of the bolt and the stopping face through tensioning.

In a surprising manner it has shown that the use of the bioelasticsynthetic material PEEK provides for ideal conditions for a permanentfusion. The elastic properties similar to those of the bone prevent theimplant from sinking in and support the fusion tendency. At the sametime, the X-ray transparency ensures optimum postoperative diagnostics,namely without requiring, as compared to the prior art, largerradiological windows in the implant material.

Suitable, also relatively small and correspondingly positioned X-raymarkers made, for example, of titanium or a titanium alloy material,allow the localization of the implant at any time.

With respect to the application and use of the implant, reference ismade to the statements set forth below.

At first, the intervertebral disc space is emptied through atransforaminal access. To this end, appropriate grasping forceps orshaped curettes known per se are used.

After the diskectomy, the intervertebral disc space is distracted bymeans of special distracters to the desired height. A suitabledistraction height is reached as soon as the distractor is under tensionand a respectively stable feeling is achieved. After the distraction,the required implant size, specifically the height of the implant isverified by means of special test implants. The positioning instrumentaccording to the invention may already be used to hold these testimplants.

Prior to the implantation of the implant, the size of which has thenbeen ascertained, an appropriate material, e.g. cancellous bone, ispreferably filled into the intervertebral disc space ventrally and intothe opposite lateral side of the implant. The portion dorsally of theimplant is filled as well.

For the implant, which is to be filled as well, a filling aid is used,into which the implant is inserted. The filling aid adopts the outercontour of the implant and defines a support frame.

After a suitable angle between the instrument and the implant was foundby means of the positioning instrument and the stopping possibility, andafter this angle was subjected to a corresponding fixation, the implantis inserted into the intervertebral disc space. Due to the implantationcurve it is recommendable to adapt during the actual implantation theangle by a brief loosening motion, by making use of the advantageouseffects of the positioning instrument.

A final positioning may be achieved by means of suited straight or bentpush-pins. To obtain a correct implantation, the convex side of theimplant is oriented ventrally and the two implant ends are orienteddorsally. To obtain all desired advantageous effects, the implant shouldbe positioned as ventrally as possible. After the implantation, the restof the intervertebral disc space is filled, so as to ensure a reliablefusion.

The principle of the implant according to the invention is based on thetension of the annulus and the longitudinal ligaments in combinationwith a sufficient bone quality. In certain cases, an additionalstabilization should be obtained by means of a dorsal fixator.

As was mentioned before, the implant may be made of a syntheticmaterial, specifically of PEEK. This material is transparent to X-rays,and its mechanical properties are very similar to those of the body. Tofacilitate postoperative diagnostics, X-ray markers may be incorporatedinto the implant. A marker is located, for example, in the ventral,medial portion of the implant in vertical orientation, and anothermarker at the tip of the implant in horizontal, sagittal orientation.Additionally, the rotary part for receiving the instrument may act as anX-ray marker.

The invention shall be explained in more detail below by means of anembodiment and with the aid of figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows various representations of the sickle-shaped implantaccording to the invention, and

FIG. 2 shows a lateral view and a perspective representation of theimplant positioning instrument.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The surface areas of the implant for the transforaminal interbody fusionof lumbar vertebral column segments according to the embodiment, whichcome into direct contact with the vertebral column, have specificstructures 1 serving as a dislocation protection. These structures 1 canhave, for example, the shape of truncated pyramids or truncated cones,or may be realized in the form of cut, spherical bodies.

The implant body itself is sickle-shaped, whereby, in case of use, theconvexity of the sickle 2 is oriented ventrally and the inner side ofthe sickle 3 is oriented dorsally.

An engagement part 4 is provided on one end of the sickle, and the otherend of the sickle opposite to this engagement part has a tapering,beak-like shape 5.

At least one filling hole 6 is provided between the sickle walls.

The engagement part 4 is formed as a piovtable or rotatable bolt , whichis located in a corresponding recess 7 in the implant.

The bolt comprises an insertion opening 8 with an inner thread (notshown), which extends substantially perpendicular to the longitudinalaxis of the bolt.

The insertion opening 8 serves to receive a respective end 9 of thepositioning instrument 10 (FIG. 2).

In the implant body, which is preferably made of a synthetic material,various X-ray markers may be incorporated, which are not illustrated inthe figures, so that a postoperative localization of the implant can beachieved at any time.

According to FIG. 2 the positioning instrument 10 is comprised of ahandle 11 with a sleeve 12.

A pin with a threaded end (part 9) is guided in the sleeve 12, whereinthe threaded end is designed complementarily with respect to the innerthread of the insertion opening 8 in the bolt.

By a rotary motion on the cap 14 the pin 9 with the threaded end can bemoved.

At the leading end of the sleeve 12 a stopping face 13 for the implantis provided, so that the implant held by the pin 9 is fixable in therespective angular position by means of the bolt and the stopping face13.

The invention claimed is:
 1. An implant for the transforaminal interbodyfusion of lumbar vertebral column segments, which comprises: a mainbody, the main body including a top surface and a bottom surfacesituated opposite the top surface, surface areas of at least one of thetop surface and the bottom surface which come into direct contact withthe vertebral column segments being formed with a dislocationprotection, the main body having a sickle shape and further including aninner side wall and a convex outer side wall situated opposite the innerside wall, and a first end portion and a second end portion situatedopposite the first end portion, the first end portion having a beak-liketapering shape, the second end portion having a throughbore formedtherein and oriented transversely in the main body in a directionbetween the top surface and the bottom surface, the main body havingformed therein at least one filling hole situated between the inner sidewall and the convex outer side wall; and an engagement part, theengagement part being formed as a bolt and being rotatably or pivotallyreceived by the transversely-oriented throughbore formed in the mainbody, the bolt having a longitudinal axis, the bolt having a side walland an insertion opening formed therein extending perpendicularly to thelongitudinal axis of the bolt, the second end portion of the main bodyhaving a access recess formed therein, the access recess being incommunication with the insertion opening formed in the bolt to allow aportion of a positioning instrument for positioning the implant betweenvertebral column segments to pass therethrough and into the insertionopening of the bolt.
 2. The implant as defined by claim 1, wherein theimplant is made of a bioelastic synthetic material.
 3. The implant asdefined by claim 2, wherein the material of which the implant is made ispolyetheretherketone (PEEK).
 4. The implant as defined by claim 1,wherein the implant includes X-ray markers situated on the main bodythereof.
 5. The implant as defined by claim 1, wherein the dislocationprotection formed on the surface areas which come into direct contactwith the vertebral column segments includes structures which have theshape of one of a truncated pyramid and a truncated cone.
 6. The implantas defined by claim 1, wherein the bolt is made of an X-ray detectablematerial.
 7. The implant as defined by claim 1, wherein the boltincludes an inner thread situated within the insertion opening formedtherein.
 8. A positioning instrument for use with the implant defined byclaim 7, which comprises: a sleeve; a pin received by the sleeve, thepin having a threaded end which cooperatingly engages the inner threadof the bolt situated within the insertion opening of the bolt so thatthe implant may be releaseably secured to the pin, the pin beingrotatable within the sleeve, the sleeve including a leading end having astopping face situated thereon, the implant being releaseably securableto the pin and having its main body fixable in a selectable angularposition with respect to the bolt by the stopping face engaging the mainbody through tensioning.